In a fabricating process of a semiconductor device in which a lamination structure of an integrated circuit is formed on a surface of a semiconductor wafer (hereinafter, referred to as a “wafer”) which is a substrate, a liquid processing process is provided to process the wafer surface using a liquid, in which for example, minute dust or a natural oxide film on the wafer surface is removed with a cleaning liquid such as, for example, a chemical liquid.
However, with high integration of the semiconductor device, when, for example, the liquid attached to the surface of the wafer is removed in the liquid processing process, a phenomenon so-called a pattern collapse becomes problematic. The pattern collapse refers to a phenomenon in which, when the liquid remaining on the wafer surface is dried, the liquid remaining at left and right sides of, for example, a convex (that is, inside of a concave) of an unevenness forming a pattern is unevenly dried, and then a balance of surface tensions that draw the convex from side to side is lost, and thus, the convex collapses in a direction in which the liquid remains in a large amount.
As a technique for removing the liquid attached to the wafer surface while suppressing occurrence of the pattern collapse, a method using a fluid in a supercritical state or a subcritical state (hereinafter, the states are integrally referred to as a “high-pressure state”) has been known. The fluid (high-pressure fluid) in the high-pressure state is lower in viscosity and higher in capability of extracting the liquid than the liquid. In addition, no interface exists between the high-pressure fluid and the liquid or gas which is in an equilibrium state to the high-pressure fluid. Therefore, when the liquid attached to the wafer surface is substituted with the high-pressure fluid and thereafter, the state of the high-pressure fluid is changed to a gas state, the liquid may be dried without being influenced by the surface tension.
The applicant has developed a liquid processing apparatus that performs a liquid processing using a single wafer-type liquid processing unit configured to supply a processing liquid to a surface of a wafer which rotates and thereafter, conveys the wafer of which the surface is covered with a dry prevention liquid to a high-pressure fluid processing unit, and removes the dry prevention liquid in a processing container. For example, in terms of high replaceability between the liquid and the high-pressure fluid and suppression of inflow of moisture in the liquid processing, Japanese Patent Laid-Open Publication No. 2011-187570 uses hydrofluoro ether (HFE) which is a fluorine-containing organic solvent (described as “fluorine compound” in Japanese Patent Laid-Open Publication No. 2011-187570) for both the dry prevention liquid and the high-pressure fluid. Further, the fluorine-containing organic solvent is suitable for the dry prevention liquid in terms of its flame-retardancy.
Meanwhile, the fluorine-containing organic solvent such as, for example, HFE, hydrofluoro carbon (HFC), perfluoro carbon (PFC), or perfluoro ether (PPE) is more expensive than, for example, isopropyl alcohol (IPA) and a volatile loss during wafer conveyance causes an increase in an operation cost. As a result, after the fluorine-containing organic solvent is used as the dry prevention liquid or the high-pressure fluid, when a mixed gas of the fluorine containing organic solvent is generated and is used through separation and regeneration, the operation cost may be reduced.
In this case, fluorine ions (F ions) may be incorporated in the mixed gas. When the F ions remain in the mixed gas, particles occur on the wafer by the F ions at the time of regenerating and using the fluorine-containing organic solvent.